This laboratory was the first to transmit non-A, non-B hepatitis (subsequently proved to be hepatitis C), and HIV to the chimpanzee and hence to establish an animal model for these infections. Current studies in this model include the following: (1) The Early Events of HIV Infection: In this study a chimpanzee was infected with HIV and serial apheresis units were obtained during the window period between exposure and the first detection of anti-HIV antibody. No markers of HIV infection were detectable until the fifth week post-exposure, when virus was detectable by measurement of HIV RNA, HIV DNA, and viral culture. In contrast, anti-HIV and p24 antigen, used in blood donor screening, were not detectable until 8 weeks post-exposure. In a second phase of the experiment, the 3, 4, and 5 week samples were sequentially inoculated into a second chimp. The 3- and 4-week samples were shown to be noninfectious, while the 5-week sample was infectious. Hence, infectivity did not precede the detection of HIV RNA and DNA, suggesting that if such assays were introduced into blood screening they might totally abrogate the infectious window and prevent blood transmission of HIV. (2) Hepatitis G Virus (HGV)- Hepatitis c Virus (HCV) Interactions: In collaboration with CDC, this study will infect HCV carrier chimps with HGV and simultaneously infect two chimps with HCV and HGV to determine if HGV facilitates the clearance of HCV as has been suggested in human studies. (3) Fulminant Hepatitis: Using samples from rare cases of fulminant hepatitis C, this study will seek to identify a virulent strain of HCV by chimp inoculation and serial passage. (4) Viral Inactivation: This study will use the chimp model to establish the safety of psoralen/UV light-inactivated platelets. This is the first viral inactivation procedure that maintains the integrity of the cellular components of blood. In vitro studies indicate that the method inactivates a broad array of viruses including HiV, hepatoviruses, and flaviviruses, the latter serving as models for HBV and HCV. If inactivation is confirmed in vivo, this method should have broad application for platelet transfusions and possibly for red cells.